Male - 11 week old fetus - 13 weeks Pregnant

Development of the male external
genitalia is dependent upon dihydrotestosterone which is produced by the
testes. As the genital tubercle is elongating and growing to form the
penis, the urogenital folds which lie on either side of the urogenital
membrane begin to move towards each other forming a groove, this is
known as the urethral groove. The urogenital folds fuse together on the
ventral side of the developing penis, enclosing what will now become the
spongy urethra.

11 week old fetus

( Fetus size = 2.5 inch, 64 mm )

With
a boy, the genital tuber will form the glans penis (4). The body of the
penis will be formed by the fusion of the urogenital folds, this fusion
is not yet completely finished (7). The scrotum (6) is formed by the
fusion of the labioscrotal folds (2). The Raphe [line] of the scrotum
(5) corresponds to the zone of fusion of the labioscrotal folds.

At
this stage of development, the testicles are located in the abdomen.
They will not go down into the scrotum (6) until about the seventh or
eighth month of pregnancy.

Female changes

In the absence of the SRY gene, of the Y chromosome, a female embryo will develop.

The
development of the female external genitalia is promoted by the
presence of estrogen and other hormones within the maternal system. The
phallus described earlier continues to grow to become the clitoris.
Meanwhile, the urogenital folds are developing into the labia minora.
Their development is similar to that in the male. They grow up along
side the phallus except that in the female, they fuse only at the most
posterior aspect (bottom) to form the frenulum labiorum pudendi or
fourchette.

The labioscrotal folds continue to grow as well,
fusing at their most posterior and anterior portions to form labial
commissures. The portions of the labioscrotal folds which do not fuse
form the labia majora.

With
girls, the genitals are formed starting from the same embryonic bodies
as those which form the male reproductive apparatus.

The urogenital and labioscrotal folds are not joined as with boys. They will respectively form the Labia minora (7)[small lips] and Labia majora (4) [large lips] of the vulva. The genital tuber will form the clitoris (3).

Ovaries
are not identifiable until after the twelfth week. In girls, the
ovaries contain over six million eggs, this decreases to approximately
one million by birth and will be reduced to about 400 by the time of
puberty.

By
the 20th week of pregnancy the external genitalia changes are done. On
ultrasound, if your baby is cooperating and is positioned in a favorable
way, his or her sex can be identified as early as the 16th to 18th week
of your pregnancy.

The
male fetus may show a round bulbous area within the genital area which
is the scrotum and penis. This sometimes can be seen on screen as an
appearance similar to the profile of a small snail.

Of course, if
your baby is 'hiding his stuff' (positioned in such a way as to prevent
identification), it will make no difference how far along in your
pregnancy you are -- you won't find out your baby's sex.

The
correct visualization of any fetal part depends on many factors such as
fetal position, amount of amniotic fluid and thickness of the abdominal
wall.

Most of the time the sonographer should be able to tell the sex of the baby by about 20 weeks of pregnancy.

The
correct visualization of any fetal part depends on many factors such as
fetal position, amount of amniotic fluid and thickness of the abdominal
wall.

The
absence of the penis must not be taken as sufficient evidence of the
fetus being a girl. Using ultrasound the 3 lines sign which denotes the
labia in the fetus is an indication of the female gender.

Ultrasound
scans done in later pregnancy or 3D scans can make it easier to see the
gender of a baby. The sonographer may not always get a good view of the
private parts of the fetus for many reasons and therefore may not be
able to give you an accurate answer.

Some sonographers are not
allowed to tell you the gender, but may show the genital area on the
screen and let you decide which sex your baby is.

The HOT topic on pregnancy forums around the world is...

The angle of the dangle topic

Q. Can they tell the sex of baby at 12 week scan ?A.
At around 12 weeks a sonographer may make a 'best guess' as to the
gender of baby from a scan, but this can, and will be, only a little
better than 50/50.

Mouseover = Rotate image

The
correct visualization of any fetal part depends on many factors such as
fetal position, amount of amniotic fluid and thickness of the abdominal
wall. The following images are not typical, as intermediate forms
exist, establishing gender can sometimes be very difficult.

Angle of the dangle

On
ultrasound, if your baby is cooperating and is positioned in a
favorable way, fetal sex can be determined during a scan when the fetus
is about 12 weeks (about 14 weeks after LMP).

The determination
is made by studying the angle between the genital 'bump' and the
direction of the lower portion of the spine. The following images are
not typical and intermediate forms do exist, establishing gender can
sometimes be difficult.

12 week old fetus - (Fetus size = 3 inch, 75 mm) - 14 weeks pregnant

Male gender

With the male fetus, the genital tubercle usually creates an angle of greater than 30° with the lower part of the spine.

Female gender

In
the female fetuses, the genital tubercle protrudes in the same
direction as the lower portion of the spine with an angle of less than
30° relative to the backbone.

How accurate are routine first trimester scans for fetal gender determination.

Ultrasound gender study
- Objective study to assess the accuracy of fetal gender determination
at a routine first trimester scan for detailed assessment of anatomy and
nuchal thickness measurement.

In the study the angle of the
genital tubercle was used to assign fetal gender. At 11 weeks there was
an error rate of 50% and only 14 of every 100 was assigned correct male
gender. In the male fetuses after 12 weeks, there was a significant
increase in the angle of the genital tubercle from the horizontal. The
accuracy of sex determination increased with gestation.